A normal heart beat initiates at the sinoatrial node, located proximal the right atrium of the heart. The sinoatrial node causes electrical impulses to spread through the right and left atria, which in turn causes the atria to contract. The impulses travel to the atrioventricular node and then through the walls of the ventricles, thereby causing the ventricles to contract. Such contractions force blood out of the heart to the lungs and body. When the heart operates under a regular pattern of electrical impulses, the heart beats at a generally constant rhythm—filling with blood and contracting in a normal fashion.
Atrial fibrillation is a common source of irregular heart rhythms. It affects millions of people in the United States, and thousand of new cases of atrial fibrillation are diagnosed each year. When a patient suffers from atrial fibrillation, irregular electrical impulses begin and spread through the atria. The resulting rhythm is disorganized and inconsistent. The atria do not contract in a regular rhythm because the impulses are traveling through the atria in a disorderly fashion.
Patients who suffer from atrial fibrillation may experience various symptoms, such as heart palpitations, a lack of energy, dizziness, chest pains, pressure or discomfort in the chest, and breathing difficulty. Some people may have atrial fibrillation without exhibiting any symptoms at all, but chronic atrial fibrillation can result in future problems including blood clotting (increased risk of suffering a stroke) and heart failure.
Various options may be used to treat atrial fibrillation and to restore normal heart rhythm. For example, a patient with atrial fibrillation may receive medications or a pacemaker device to prevent blood clots and control the heart rate. In some circumstances, heart surgery may be performed to treat atrial fibrillation. For example, the Cox-Maze procedure is a surgery that may require an incision in the patient's sternum, and in many instances, requires a heart-lung machine to oxygenate and circulate the blood during surgery.
Another treatment option is catheter ablation therapy. For example, a catheter may be used to perform pulmonary vein isolation ablation, in which a circular balloon at the tip of the catheter is inserted into the pulmonary vein. Material in the balloon at the tip of the catheter is then heated to ablate tissue inside the pulmonary vein. A circular scar is formed in the pulmonary vein as an attempt to create a conduction block to stop passage of irregular impulses firing from within the pulmonary vein. Forming the scar tissue inside the pulmonary vein is not always successful at preventing atrial fibrillation.
The design of the catheter ablation device has an effect on the success rate of the catheter ablation procedures. One factor that affects the design of the catheter ablation device is the efficacy of delivering the ablating energy. If, for example, the catheter device is improperly sized or unable to adjust to the contours of the target tissue, some portion of the target tissue may remain after the ablating procedure. The living tissue may not block the irregular impulses from the pulmonary vein to the atrium, thus permitting future occurrences of atrial fibrillation.
Another factor that affects the design of the catheter ablation device is the isolation of the ablating energy. If, for example, the catheter ablation device does not properly isolate the ablating energy to the target tissue or delivers excess energy, some live tissue in a non-targeted area may be unnecessarily destroyed. In such circumstances, the catheter ablation procedure may cause pulmonary vein stenosis (a narrowing of the passageway), which may result in more serious cardiovascular problems for the patient.